This invention relates to the preparation of phenylenediamines and in particular p-phenylenediamine which is used, for example, in the production of aromatic polyamide-based fiber reinforcing materials.
The preparation of phenylenediamines by the ammonolysis of chlorobenzenes in the presence of a copper catalyst is well known to the art and is described, for example, in British Patent No. 3875 and Jour. Am. Chem. Soc., Vol. 20, pp. 1033-1042 (1920). Although satisfactory conversion of dichlorobenzene to phenylenediamine is typically obtained, the phenylenediamine is difficult to isolate from the reaction mixture and unsatisfactory low yields of a relatively impure product are obtained if, for example, the reaction mixture is simply dehydrated. The phenylenediamine may be separated in the form of its hydrochloride salt, however, difficulties are also encountered in converting the salt form to the free amine.
Japanese patent application Ser. No. 011,327, published Aug. 11, 1977, describes extracting free phenylenediamine from a crude aqueous alkaline ammonolysis reaction mixture with C.sub.3 and C.sub.4 aliphatic alcohols. However, since these alcohols are appreciably water soluble and tend to form azeotropic mixtures with aqueous solutions, it is doubtful whether substantially complete recovery of phenylenediamine product could be obtained from the extract without the expedient of, for example, azeotropic distillation.